Energy flows in stellar coronae

太阳是我们唯一可以详细研究的星星，从它的内部到外层大气（日冕）和太阳风，太阳风弥漫在整个太阳系中。日冕也是一个独特的实验室，我们可以用来了解整个宇宙中发生的基本等离子体过程（其中大部分是由磁化等离子体组成）。太阳辐照度和粒子通量从根本上影响空间天气、大气层和地球的全球气候。然而，到目前为止，我们还没有理解关于太阳（以及一般恒星）的许多基本问题。太阳的标准模型最近受到了质疑。我们仍然不知道将太阳日冕加热到数百万度的主要机制，导致耀斑和爆发，加速粒子，产生极紫外线（EUV）中最强的辐射。我们对极紫外线或X射线的太阳辐照度及其对地球气候的潜在影响也知之甚少。至于其他恒星，我们知道大多数都有强烈的X射线发射，但产生这些X射线的过程仍然是未知的。这是太阳日冕物理学的黄金时代，最近的任务（SOHO，TRACE，RHESSI）收集了大量数据，现在补充了Hinode（Solar-B），很快还有STEREO，SDO。两台EUV光谱仪（SOHO/CDS，Hinode/EIS）有英国的大力参与。我认为，现在是时候投入更多的资源来分析和解释这些光谱数据了，因为它们是推进我们对日冕理解的关键。目前的灵敏度和分辨率的EIS将允许新的研究。特别是，我打算耦合观测与理论建模，以了解哪些过程占主导地位的能量释放和流动的电晕，考虑到非平衡和非热效应的等离子体。特别是，我将研究加热的位置和演变的日冕环的磁场的变化，和耀斑期间的能量流，色球蒸发。光谱观测和现实的大气模型也将揭示为什么最亮的EUV线如此明亮的问题，因此在未来我们也将能够预测它们的发射。我还计划使用独特的10年之久的SOHO观测，首次研究EUV光谱辐照度及其随太阳周期的变化。然后我们将能够研究对全球气候的任何可能影响。通过同样的观测，我还将获得最后一个周期中日冕的物理特征。有了这些和一些建模，就有可能详细模拟来自其他恒星的X射线发射。通过这些模拟，以及钱德拉和XMM-牛顿对不同年龄恒星的观测，将有可能理解在哪些情况下观测到的X射线发射可能是由于类似于活跃太阳的热日冕的存在。提供准确的原子数据是本提案的一个组成部分，因为它们对等离子体诊断和建模非常重要。我计划继续研究EUV和X射线的离子，并提供原子数据，以研究非平衡和非热效应，这在日冕中可能很重要。

The Sun is the only star that we can study in detail, from its interior to the outer atmosphere (corona) and the solar wind, which permeates the entire solar system. The solar corona is also an unique laboratory that we can use to understand fundamental plasma processes that occurr throughout the universe (most of which is composed of magnetised plasma). The solar irradiance and particle flux fundamentally affect space weather, our atmosphere and the global climate of our planet. Yet, we have so far failed to understand many fundamental questions about the Sun (and stars in general). The standard model of the Sun has recently been called into question. We still do not know the prime mechanisms that heat the solar corona to millions of degrees, that cause flares and eruptions, that accelerate particles, that produce the strongest emission in the Extreme Ultra Violet (EUV). We also know very little about the solar irradiance in the EUV or X-rays, and its potential effects on the global climate of our planet. As for other stars, we know that most have strong X-ray emission, however the processes that produce these X-rays are still largely unknown. This is a golden age for the physics of the solar corona, with a wealth of data gathered by recent (SOHO, TRACE, RHESSI) missions, now complemented with Hinode (Solar-B), and soon with STEREO, SDO. The two EUV spectrometers (SOHO/CDS, Hinode/EIS) have a strong UK involvement. I believe that it is timely to invest more resources into the analysis and interpretation of these spectroscopic data, because they hold the key to advance our understanding of the solar corona. The current sensitivity and resolution of EIS will allow novel studies. In particular, I intend to couple observations with theoretical modeling to understand which processes dominate the energy release and flow in the corona, by taking into account non-equilibrium and non-thermal effects in the plasma. In particular, I will study the location and evolution of heating in coronal loops in relation with the changes of the magnetic field, and energy flows during flares, in relation to chromospheric evaporation. Spectral observations and realistic atmospheric models will also shed light on the problem of why the brightest EUV lines are so bright, so in the future we will also be able to predict their emission. I also plan to use the unique 10-year long SOHO observations to characterise for the first time the EUV spectral irradiance and its variations with the solar cycle. We will then be able to study any possible effects on global climate. With the same observations I will also obtain the physical characteristics of the solar corona during the last cycle. With these and some modeling, it will be possible to simulate in detail the X-ray emission from other stars. With these simulations, and Chandra and XMM-Newton observations of stars of different ages, it will be possible to understand in which cases the observed X-ray emission could be due to the presence of a hot corona similar to an active Sun. Provision of accurate atomic data forms an integral part of this proposal, given their importance for plasma diagnostic and modeling. I plan to continue the work on the ions for the EUV and X-rays, and to provide atomic data to allow studies of non-equilibrium and non-thermal effects, which are presumably important in the solar corona.